Patients with OSA may experience recurrent apnoeas or hypopnoeas during sleep that are only terminated by the patient arousing. These recurrent respiratory dysfunction events cause sleep fragmentation and stimulation of the sympathetic nervous system. This can have severe consequences for the patient including day-time sleepiness (with the attendant possibility of motor-vehicle accidents), poor mentation, memory problems, depression and hypertension. Patients with OSA are also likely to snore loudly, thus also disturbing their partner's sleep.
Patients may also experience other events that may interrupt sleep. For example, Periodic Limb Movement (PLM) is a repeated cramping or spasm of the legs during sleep. These leg movement events may be considered a sleep disorder when they disrupt sleep and lead to daytime sleepiness.
Patients with OSA are typically treated with constant positive airway pressure (CPAP). The positive pressure prevents collapse of the patient's airway during inspiration, thus preventing recurrent respiratory system events (e.g., apnoeas or hypopnoeas) and their sequelae. Such a respiratory treatment apparatus can function to supply the patient with a supply of clean breathable gas (usually air, with or without supplemental oxygen) at the therapeutic pressure or pressures, at appropriate times during the subject's breathing cycle.
Respiratory treatment apparatus typically include a flow generator, an air filter, a mask or cannula, an air delivery conduit connecting the flow generator to the mask, various sensors and a microprocessor-based controller. The flow generator may include a servo-controlled motor and an impeller. The flow generator may also include a valve capable of discharging air to atmosphere as a means for altering the pressure delivered to the patient as an alternative to motor speed control. The sensors measure, amongst other things, motor speed, gas volumetric flow rate and outlet pressure, such as with a pressure transducer, flow sensor or the like. The apparatus may optionally include a humidifier and/or heater elements in the path of the air delivery circuit. The controller may include data storage capacity with or without integrated data retrieval/transfer and display functions.
While these devices may typically be configured to detect sleep disordered breathing events of the apnea or hypopnea type, they do not usually provide more detailed information to the user about sleep. Thus, it may be desirable to develop methods and apparatus for detecting these and other conditions of sleep to more completely assess sleep quality.